Two hundred and twenty-eight blood samples from 154 HIV-seropositive subjects were investigated for the presence of HIV in peripheral blood mononuclear cells (PBMC) and plasma (without prior ultracentrifugation or filtration), using normal PBMC as the target for replication. HIV was recovered from PBMC and plasma in 80.5 and 19.5% of the patients, respectively. Plasma viraemia was significantly associated with clinical manifestations of HIV infection, indicating that HIV replication increased as disease progressed. This was confirmed by the statistically significant correlations between plasma viraemia and low CD4 cell counts (P<0.01) and low anti-p24 antibody titers (P<0.01). On patient follow-up, detection of HIV in plasma was transient. p24 antigenaemia was only detected in 13.6% of cases and was also associated with advanced clinical stages of the disease. When HIV RNA detection by polymerase chain reaction (PCR) was compared with plasma viraemia, HIV RNA was detected in plasma in all symptomatic cases and in 53.8% (seven out of 13) of asymptomatic patients [Centers for Disease Control (CDC) stages II and III], confirming that PCR was far more sensitive than plasma culture. These results indicate that cell-free virus production is associated with the clinical stage of HIV infection and may serve as a marker for disease progression. Detection of HIV RNA by PCR appears to be the most sensitive method to detect viraemia.